The structures of trans-dichloro- and trans-bis(isothiocyanato)nickel(II) complexes with 1,4,8,11-tetraazacyclotetradecane, 1,4,8,12-tetraazacyclopentadecane, and 1,5,9,13-tetraazacyclohexadecane. The negative correlation between the axial and in-plane co

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The molecular structures of the six titled compounds, which contain 14-membered, 15-membered, or 16-membered tetraazamacrocyclic ligands, have been determined by single crystal X-ray analyses. On going from smaller to larger rings, the average in-plane Ni–N distance increased by 0.05–0.06 Å for each ring member added. For a series of complexes with given axial ligands (X), the mean axial coordination bond length (Ni–X) was found to decrease as the average in-plane distance (Ni–N) increased. The degree of the negative correlation was stronger for complexes with weaker axial ligands (Cl<SUP>−</SUP>) than for those having stronger axial ligands (NCS<SUP>−</SUP>). Similar negative interrelationships between the Ni–X and Ni–N distances have been found for complexes which have the same in-plane macrocyclic ligand, but different axial ligands. The molecular stereochemistries of the complexes have been discussed. For all the complexes with the 1,4,8,12-tetraazacyclopentadecane ligand, a structural disorder of the same type has been found: gauche five-membered and skew six-membered chelate rings are randomly interchanged in the crystal. This arises mainly from the similarity of the bite angles of the five- and six-membered chelate rings in the gauche and the skew conformations respectively.
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